Railroad freight cars may be constructed with side beams that carry distributed lading loads to the end sections of the cars. In a deep side beam the top chord typically carries compressive loads, and the side sill, which typically defines the bottom chord of the beam, carries loads in tension. Since the side sill is a primary structural member in a well car, it may be desirable to avoid conditions that may impair its function, or that may give rise to unexpected or unknown secondary loading conditions.
One type of car in which a deep side-beam performs this role is an intermodal well car. A well car body is required to withstand three kinds of loads. First, it must withstand longitudinal draft and buff loads inherent in pulling or pushing a train, particularly those loads that occur during slack run-ins and run-outs on downgrades and upgrades, and single-ended impact load. Second, the well car must support a vertical load due to the trailers or shipping containers it carries. Third, it must be able to withstand lateral or roll loading as the well car travels along curves and switch turn-offs.
The floor structure of a container carrying well car includes lading bearing cross members (a) at the ends of the well in the 40 foot container pedestal positions, and (b) in the middle of the well in the form of a central cross member to support containers at the 20 foot position. These vertical load bearing cross members support the shipping container corners. The floor structure may also include several intermediate cross members, and diagonals.
The loads transmitted by the floor structure are carried into the side beams, and from the side beams into the end sections of the car. The end portions of the side beams are typically shallow, with a cut-out, or relief, to accommodate motion and maintenance access of the truck that supports the end of the car. In the end portion of the car the vertical loads flow to the centerplate, or equivalent structure, whence they are carried into the truck and, ultimately, reacted by the rail and roadbed.